1. Field of the Invention
Numerous deposit-forming substances are inherent in hydrocarbon fuels. These substances when used in internal combustion engines tend to form deposits on and around constricted areas of the engine contacted by the fuel. Typical areas commonly and sometimes seriously burdened by the formation of deposits include carburetor ports, the throttle body and venturies, engine intake valves, etc.
Deposits adversely affect the operation of the vehicle. For example, deposits on the carburetor throttle body and venturies increase the fuel to air ratio of the gas mixture to the combustion chamber thereby increasing the amount of unburned hydrocarbon and carbon monoxide discharged from the chamber. The high fuel-air ratio also reduces the gas mileage obtainable from the vehicle.
Deposits on the engine intake valves when they get sufficiently heavy, on the other hand, restrict the gas mixture flow into the combustion chamber. This restriction, starves the engine of air and fuel and results in a loss of power. Deposits on the valves also increase the probability of valve failure due to burning and improper valve seating. In addition, these deposits may break off and enter the combustion chamber possibly resulting in mechanical damage to the piston, piston rings, engine head, etc.
The formation of these deposits can be inhibited as well as removed by incorporating an active detergent into the fuel. These detergents function to cleanse these deposit-prone areas of the harmful deposits, thereby enhancing engine performance and longevity. There are numerous detergent-type gasoline additives currently available which, to varying degrees, perform these functions.
Two complicating factors have, however, recently arisen. First, with the advent of automobile engines that require the use of nonleaded gasolines (to prevent disablement of catalytic converters used to reduce emissions), it has been found difficult to provide gasoline of high enough octane to prevent knocking and the concomitant damage which it causes. The chief problem lies in the area of the degree of octane requirement increase, herein called "ORI", which is caused by deposits formed by the commercial gasoline.
The basis of the ORI problem is as follows: each engine, when new, requires a certain minimum octane fuel in order to operate satisfactorily without pinging and/or knocking. As the engine is operated on any gasoline, this minimum octane increases and, in most cases, if the engine is operated in the same fuel for a prolonged period, will reach an equilibrium. This is apparently caused by an amount of deposits in the combustion chamber. Equilibrium is typically reached after 5000 to 15000 miles of automobile operation.
The octane requirement increase in particular engines used with commercial gasolines will vary at equilibrium from 5 or 6 octane units to as high as 12 or 15 units, depending upon the gasoline compositions, engine design and type of operation. The seriousness of the problem is thus apparent. A typical automobile with a research octane requirement of 85, when new, may after a few months of operation require 97 research octane gasoline for proper operation, and little unleaded gasoline of that octane is available. The ORI problem also exists in some degree with engines operated on leaded fuels. U.S. Pat. Nos. 3,144,311; 3,146,203; and 4,247,301 disclose lead-containing fuel compositions having reduced ORI properties.
The ORI problem is compounded by the fact that the most common method for increasing the octane rating of unleaded gasoline is to increase its aromatic content. This, however, eventually causes an even greater increase in the octane requirement. Moreover, some of presently used nitrogen-containing compounds used as deposit-control additives and their mineral oil or polymer carriers may also significantly contribute to ORI in engines using unleaded fuels.
It is, therefore, particularly desirable to provide deposit control additives which effectively control the deposits in intake systems of engines, without themselves eventually contributing to the problem.
The second complicating factor relates to oil solubility of the fuel additives. Fuel additives, due to their higher boiling point over gasoline itself, tend to accumulate on surfaces in the combustion chamber. This accumulation of the additive eventually finds its way into the lubricating oil via a "blow-by" process. In some cases this process may be of no concern as the fuel additives will be inert and compatible in the oil. However, if the additive is incompatible in the lubricating oil a serious problem develops as the accumulation of the additive results in an emulsion-like sludge which is detrimental to efficient operation. Therefore, it is particularly desirable that the gasoline additive be oil compatible.
2. Prior Art
Polyether amine-type fuel additives for deposit control are well-known but have traditionally been surfactant-type molecules having a large, non-polar hydrophobic end or "tail", for instance, a hydrocarbyl capped polyether moiety, and a polar, hydrophilic amine or polyamine end. Examples of these type of compositions may be found in U.S. Pat. Nos. 4,247,301; 4,160,648; and application U.S. Ser. No. 403,607, Campbell, filed July 7, 1982. In the present invention, however, a composition has been discovered which in gasoline fuel functions as a deposit control additive which has a single hydroxyl group in the non-polar hydrophobic portion of the molecule. These additives contain block co-polymer polyethers in which there is no hydrocarbyl cap. Moreover, this additive is compatible in the lubricating oil.